The major goals of this project are to quantify rates of transmethylation, remethylation, transsulfuration, and cysteine turnover in healthy men and women without evidence of vitamin B6, B12 or folate deficiency and characterized for genetic mutations in methylenetetrahydrofolate reductase and cystathionine (-synthase, and secondly, to determine whether or not apparent gender differences in methionine metabolism do exist thereby accounting for the reportedly lower homocysteine levels in premenopausal women.